1. Field of the Invention
The present invention relates to a sheet skew feeding correcting apparatus capable of correcting skew feeding of a conveyed sheet, and an image forming apparatus equipped with the sheet skew feeding correcting apparatus.
2. Description of the Related Art
Conventionally, in an image forming apparatus and its peripheral devices, skew feeding of a sheet is corrected so that an image and the sheet are aligned to correct positions for an output image which is a deliverable, and image quality is maintained. In this regard, there are proposed several sheet skew feeding correcting apparatuses which correct skew feeding of sheets only by a conveying force of a sheet without using an actuator.
For example, Japanese Patent Laid-open No. 2000-233849 proposes a configuration where a force is applied to a shutter member, the shutter member is turnably supported on the roller shaft of one of a pair of rollers, and the leading end of a conveyed sheet strikes the shutter member. The shutter member is turned and pushed opened by an abutting force from the leading end of the conveyed sheet, and the skew feeding of the sheet is corrected at that time. The sheet whose skew feeding was corrected is nipped and conveyed between the pair of downstream rollers.
To avoid a difference in timing of a shutter opening operation caused by a firmness difference between sheets, there is also proposed the configuration having a shutter locking member which restricts the shutter member, and the locking member is unlocked by a loop of the sheet. According to this configuration, the shutter is operated only when the loop reaches a predetermined value.
In the shutter configuration, however, it is necessary to turn the shutter against a force applied to the shutter using an abutting force of the leading end of the sheet. The abutting force of the leading end of the sheet is prone to be influenced by the state of a sheet (e.g., firmness of a sheet). Therefore, there is the unwanted possibility that if firmness of a sheet is weak, the shutter cannot be turned, and if firmness of a sheet is strong, the shutter may be turned with skew feeding insufficiently corrected.
In the configuration where the locking member of the shutter is unlocked by a loop of a sheet, there is the unwanted possibility of the loop buckling from a friction force between the locking member and the shutter member, resulting in operation failure of the shutter.